How the 19-year-old brain can both awe and appall us

Among the most mysterious things on the planet is the brain of a male in his late teens. It has been designed by evolution for purpose without much perspective, passion without much reason, reproduction without much responsibility and performance without caution. If it was a car, it would be a Corvette convertible with 430 horsepower, no seat belts or brakes and a horn that blared, “Hey, babe, wanna go for a ride?”

That’s why we send their owners to goal lines and front lines, but don’t let them drink until they are 21. That’s why we love having them as sons but are reluctant to have them date our daughters. And as we were reminded last Monday in Boston’s marathon, it’s why we should not be surprised that among the millions of teen males growing up around us, one of them seems like a great kid one day and — under the influence of an influential, older ringleader — does something stupid, crazy or appalling the next.

Neuroscientists and other brain experts now know what the rest of us need to understand about brain biology: Those 19-year-old brains, while capable of doing things with some adult capability and many adult consequences, are not the same as fully developed adult brains. The typical brain of the late adolescent has at least three to five more years of development to go before judgment, impulse control, insight, good risk and consequence appreciation, consistent assumption of responsibility and emotional control are fully “wired” and fully functional. Neurons remain to be connected, frontal lobe nerve fibers remain to be coated with myelin so that judgment function routinely and effectively precedes decision function, and the brain wiring for full maturity is completed. (Some of you women would say all that never happens in men.)

Evidence of this incomplete development fills our living rooms with sprawled teenage males about to turn 20 with little sense of what they want to do when they grow up, and our parental lives with wonderful or painful chaos. It fills our legal systems with troubled teenagers on the verge of growing up too fast by being sentenced as adults, and our graveyards with premature deaths of 18- to 24-year-olds by the thousands in America each year. These young “boys-into-men” have among the highest crash, crime and chaos rates of our entire population.

At the same time, they go into battle for us, haul injured comrades out of harm’s way and fill our chests with pride and our eyes with tears because they can be so glorious to behold. Prince or pain; we are not certain which they will be, or when they will be whatever, because they often don’t know either and they often can be both for several difficult years.

Those who lead men in battle get all of this. Nineteen-year-olds may fill many of the ranks in our armed forces, but they don’t fill the ranks of the military’s special forces. A lot of women get this; 19-year-old males may be great material for a fling, and you might tattoo one of their names on your rear, but few of them are great material for marriage at that age. Many teachers get this, and the great ones see their role as helping these young men find their own path of exploration and learning that leads from aimless wandering and frustration to purpose with passion, tempered by reason. Society is slowly starting to get this, which is why there is a federal drinking age that starts at 21, those under 21 often cannot buy homes or rent cars, and so forth.

What society has not done is turn that slowly growing awareness into real social policy. Few other than parents, teachers, the military and law enforcement or others in the criminal justice system pay much attention to those young men making the turn from adolescence into adulthood. Too few of the rest of us are watching those teens and early 20-somethings in transition closely enough to make sure the troubled ones get help more than punishment when they make wrong turns, more support than scolding or mental health counseling instead of explosives and assault rifles as the answer to their troubled thoughts.

Until we do, we will continue to miss the chances to stop some of them from exploding in our midst.